A content addressable memory (CAM) is unique in terms of the way in which it accesses stored data. In more traditional forms of memory, each data item is assigned a specific memory address. This address is then used as a basis for performing all storage and retrieval operations for that item. CAM-type memories, however, take an entirely different approach.
Instead of accessing data by memory address, the value of the data itself determines how it is accessed and in some cases where the data is stored or otherwise indexed. In order to implement this alternative addressing scheme, value-matching logic compares input data to the data stored in each storage location of the memory. An indicator signal is then generated to identify the location(s) where a match (or “hit”) exists. Subsequent operations (e.g., read) may then be performed on the data stored at these locations.
Content addressable memories are also known as associative memories and may be used to form the basic components of many circuits including caches, memory management units, and translation look-aside buffers. CAMs are also used in TCP/IP acceleration chips and networking chips to, for example, form look-up tables and support packet forwarding and classification operations in switches and routers.